Assessment of Flood Susceptibility and Effects on Urban Areas: A Case Study of Part of Mahananda River Basin

The paper is concerned with flood susceptibility mapping and inundation modeling and is limited to the northern sector of Mahananda river basin which falls partly in the Darjeeling and Jalpaiguri district of West Bengal, India. Comparing Analytical Hierarchy Process (AHP) and HEC-RAS modeling, the research assesses flood risk and depth in areas of hydrological sensitivity situated on slopes in the northern regions and plains in the southern regions. From the derived GIS maps of the influence factors including elevation, slope, LULC, soil, rainfall, and drainage density, multi-criteria decision analysis was conducted in order to produce a map showing flood susceptibility. In flood depth assessment, HEC-RAS was used in order to combine cross section of rivers, flow, and altitude data in order to estimate flood extent and flood depth and velocity along the river at different time of occurrence. Given below findings suggest that the western Jalpaiguri is more exposed to flood risks when compared to the eastern Darjeeling area primarily because of its flat topography. The GIS and hydraulic modeling analysis also reveals moderate to high risk along the river slope particularly where slopes are steep then gradual. The proposed integrated approach may improve the understanding of flood risks, contribute insights into efficient policies regulating urban growth across the floodplains and assist climate change adaptation for the advantage of the local government and other stakeholders aiming for protection of this environmentally sensitive area.